Conformity Magazine - January 2009 - (Page 19) ESD Open Forum ordered, although minimum quantities are often required. An important consideration and discussion to have with your suppliers is the hardness and brittleness differences of sheet stock, extruded stock and plain stock. The different processes can alter these characteristics, making a difference in wear characteristics. Usually, injection molding of parts is not a requirement for fixtures and jigs due to the limited quantities required. However, through commercialization of standardized fixtures and jigs, some parts may be injection molded and should have the ESD requirements specified during the design phase. Unfilled materials and filled materials do not mold the same, and usually the molds are different due to different shrink rates. Molding of these materials may also change the hardness or brittleness of the materials. With all of the materials and compounds available today, unless a process has some rather unusual requirements, most fixture and jig designs can incorporate the proper materials to afford the best ESD control for the applications. A good starting point in an internet search is to look for “ESD plastics.” Table 1 above should help you get started in your search for fixture and jig fabrication materials. References • D. Bellmore, “Controlling ESD in Automated Handling Equipment,” EOS/ESD Symposium Proceedings, ESD Association, Rome, NY, September 2002. • Machinery Handbook, 24th Edition. About the Author This article was written on behalf of the ESD Association by Donn G. Bellmore, CBA Corporate ESD Specialist and Reliability Analyst, Quality and Reliability Dept., Universal Instruments Corporation. Donn has worked in the ESD field for 23 years and is currently responsible for the required process and materials research, design, and integration of ESD controls in automated assembly equipment manufactured at Universal Instruments Corporation. Donn has been an active member of the ESD Association since 1995. He participates on the Garments and Ionization Committees, is a member of the Standards Committee and is the Working Group Chair for the Handlers committee. He is currently an elected Director and serves as Sr. Vice President of the ESD Association. About the ESD Association Founded in 1982, the ESD Association is a not for profit, professional organization dedicated to furthering the technology and understanding of electrostatic discharge. The Association sponsors educational programs, develops ESD standards, holds an annual technical symposium, and fosters the exchange of technical information among its members and others. Additional information may be obtained by contacting the ESD Association, 7900 Turin Rd., Bldg. 3, Rome, NY 13440-2069 USA. Phone: 315-339-6937. Fax: 315-339-6793. Email: info@esda.org. Website: www.esda.org. Brand Name for Reference Delrin Generic Name / Filler Acetal (Delrin) Homopolymer 5% to 10 % Carbon , Nanotubes and other additives Polyetherimide Graphite nanotubes Ultra High Density Polyethylene (HDPE) Dissipative Polycarbonate – 15 % Carbon Polycarbonate – Tunable Graphite nanotubes Applications Nozzles, Grippers, Guides, Covers, Clamps, Gears Nozzles, Grippers, Clamps, Locators Guides, Chutes, Rails, Locators Nozzles, Grippers, Guides Nozzles/Grippers/Guides Guides, Chutes, Rails, Locators Nozzle Bodies & Guides Nozzles, Grippers, Locators Guides & gears Guides, Chutes, Rails, Locators, covers Dissipative Foams Covers, chutes, slides, Locator pins, Nozzle Tips and Tips Locator pins, Nozzle Tips and Tips Machinability Good Surface Resistance Ohms 104 to 109 ULTEM UHMW Poor Good Poor Good Fair Fair Fair Good Poor poor Fair NA NA 104 to 106 105 103 to 106 105 to 109 102 to 106 104 103 104 104 108 104 104 106 POM Vespel Semitron Acetal EFI Royalstat Cerastat Cermax Acetel (POM) 20% Carbon Powder Graphite Polyimide Polyetherimide Polyoxymethylene (POM) Peek Carbon Fiber Urethane, Dissipative ABS/PVC Carbon Powder / Graphite Fibers Ceramic Ceramic Table 1: Materials, applications and properties JAnUAry 2009 Conformity 19 http://www.esda.org
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.